One of the stated goals of the NEI Audacious Goal Initiative in addressing the technical needs and opportunities for imaging the visual system (U01) is to develop new technology for the non-invasive measurement of retina function in vivo as related to natural vision, including visualization of metabolism at the cellular level and electrical activities. Based on strong newly acquired preliminary data, this application proposes the development of a new instrument that can image the retina in exceptional detail that together with two highly sensitive related tests can be used to evaluate retinal function. The specific aims are: (A) with a mouse two-photon ophthalmoscope (TPO), develop a novel diagnostic paradigm used to assess two functional aspects of vision: the metabolic flow of retinoids through the retinoid cycle and visual sensitivity. Along with mass spectrometric analyses, we will define critical intersections between images, structure, function and toxic molecules that affect the retina and identify potential therapies that preserve this neural tissue; and (B) develop and test a TPO imaging and diagnostic tool in humans. Initial tests will be done in a surrogate monkey/pig eye and then with the knowledge gained, we will image the eyes of individuals with advanced stages of blinding retinal diseases. Despite its' `audacity', this proposal can realistically be completed during the funding cycle. The scientific questions and interim milestones required to make this program successful are presented herein.